An aircraft may include various types of rotating electric machines such as, for example, generators, motors, and motor/generators. Many of these electric machines include various mechanical components that rotate, and may thus be supplied with lubricant. In addition, some of the components within these machines may generate heat due to either, or both, frictional losses and electrical losses, and thus may be supplied with a cooling medium. The lubricating and cooling media may be supplied from a single system that supplies a fluid, such as oil, that acts as both a lubricating and a cooling medium. As may be appreciated, the heat produced in an electric machine may be related to the output of the machine. This machine output can be independent of its rotational speed, and is typically less than the maximum output capability of the machine for most of machine operating cycles.
Many present lubricating and cooling systems are configured to either supply a relatively constant fluid flow rate to its associated electrical machine, or a fluid flow rate that varies directly with electric machine rotational speed. Moreover, these systems are typically designed for maximum machine output and losses under all operating conditions. Although generally safe, reliable, and operationally robust, this configuration does exhibit certain drawbacks. Namely, this can result in relatively high flow rates into and through the electric machine than what may be needed for most machine operating cycles, and thus can result in relatively higher windage losses and pumping power requirements, and lower machine efficiency.
Hence, there is a need for a fluid supply control system for electric machines, such as aircraft motors, generators, and starter-generators that regulates the flow rate of fluid into and through the electric machines to only what may be needed for present machine operating conditions and/or reduces windage losses and/or pumping power requirements in the electric machines and/or increases machine efficiency. The present invention addresses at least these needs.